In order to increase the output power with respect to the predetermined number of charges by improving the above-mentioned problems, Korean Patent No. 1337545 (“Ultra-short Terahertz Pulse Generator Having Multiple Foils”, Nov. 29, 2013 hereinafter referred to as related patent) filed and registered by the present applicant has been disclosed.
The configuration of the device for generating an ultra-short terahertz wave disclosed in the related patent will be briefly described as follows. Unlike the case where a single conducting foil is used in the related art, in the related patent, multiple conducting foils are arranged in parallel at a predetermined interval. At this time, the diameter of the conducting foils is gradually reduced so that the overall shape of the conducting foils becomes conical. If the ultra-short electron beam bunch of the relativistic speed passes through the conducting foils laid in layers, the electromagnetic waves spreading in a concentric circle are generated in the spaces between the respective conducting foils. Thus, the electromagnetic waves generated between the plies of the respective conducting foils are joined at the ends of the conducting foil piles having the conical structure and radiated to a free space in a conical wavefront, and the polarization of the radiated wave is directed to a central part. FIG. 1 is a simplified configuration diagram of a device for generating an ultra-short terahertz wave including conical multiple foils disclosed in the related patent. As shown in FIG. 1, when an electron beam traveling direction is a z direction, the wavefront of the radiated terahertz wave forms a cone.
The apparatus according to the related patent has a great effect of realizing the generation of a terahertz wave of more than tens of times stronger than that of the device of generating a coherent transition radiation using a single foil. That is, the above related patent is a technique that has a great effect to solve the above-mentioned problem of increasing the power of the existing terahertz source. However, as described above, the terahertz wave generated by the related patent has a donut-shaped wave form in which the wavefront is a conical shape, and no output is in the center of the wave. As a result, there is a limit in applying the related patent in the case of applications which wants a uniform distribution or linear polarization.